What we know—and don’t know—about the safety of eating GMOs

The conventional answer is "yes," and it's not hard to see why. Since their introduction in 1996, genetically modified (GM) or genetically engineered (GE) corn and soy seeds quickly conquered U.S. farm fields. Today, upwards of 70 percent of corn and 90 percent of soy are genetically modified, and these two crops form the basis of the conventional U.S. diet. Nor are they GM technology's only pathway onto our plates. Nearly 80 percent of U.S. cotton is now genetically engineered, and cottonseed oil has emerged as a staple fat for the food industry. (USDA has figures on this.) Canola oil -- another crop that has largely succumbed to genetic modification -- is yet another common ingredient.

Given their swift path to ubiquity, wouldn't we know by now if GMOs posed some threat? Since no obvious problems have come to the fore, some scientists -- and certainly the agrichemical industry, which dominates GM seed production -- have seen fit to declare them safe. Pamela Ronald, professor of plant pathology at the University of California, Davis, recently summed up the conventional view: "After 14 years of cultivation and a cumulative total of two billion acres planted, GE crops have not caused a single instance of harm to human health or the environment."

Let's leave aside Ronald's claim about the environment (which is rendered suspect by the rise of herbicide-resistant "superweeds") and dig into the human-health aspect. What we do know is that GMOs are not acutely toxic to eat. That is, we know that if you dine on a burger made from cows gorged on GM corn and soy, French fries cooked in oil from GM cottonseed, and soda laced with high-fructose syrup from GM corn, you're not likely to keel over in agony. Tens of millions of people do it every day.

But what about more subtle, long-term effects -- problems that public-health professionals call "chronic"? Here we enter less certain territory. With our highly processed diets largely deficient in fruits and vegetables, Americans have high and rising rates of chronic diseases like obesity and heart disease. Meanwhile, food allergies, autism, and non-alcohol-related liver disease have rocketed. It's highly plausible that GMOs, which have existed in our diets for less than a generation, have emerged as another of many contributors to such long-term conditions.

So GMOs could theoretically be unsafe to eat. What does science tell us about the matter? Unfortunately, not much. Back in 1992, before the first GM seed had been commercially planted, the FDA declared GM foods to be "generally regarded as safe" -- despite a complete absence of rigorous testing. And that meant that safety testing is completely unnecessary if, say, Monsanto wants to bring a novel crop to market. In a peer-reviewed 2004 paper [PDF] -- which remains an extremely useful primer on regulation of GM crops -- William Freese and David Shubert show that the FDA made the "generally regarded as safe" decision over the objections of several agency scientists, who saw significant potential for harm. Moreover, when the agency rubber-stamps the introduction of a GM crop into the food supply, it does so using extremely non-committal language. As Freese and Shubert put it:

The review process outlined above makes it clear that, contrary to popular belief, the FDA has not formally approved a single GE crop as safe for human consumption. Instead, at the end of the consultation, the FDA merely issues a short note summarizing the review process and a letter that conveys the crop developer's assurances that the GE crop is substantially equivalent to its conventional counterpart.

The authors quote from the letter the FDA sent to Monsanto on approval of Bt corn back in 1996:

Based on the safety and nutritional assessment you have conducted, it is our understanding that Monsanto has concluded that corn products derived from this new variety are not materially different in composition, safety, and other relevant parameters from corn currently on the market, and that the genetically modified corn does not raise issues that would require premarket review or approval by FDA. ... as you are aware, it is Monsanto's responsibility to ensure that foods marketed by the firm are safe, wholesome and in compliance with all applicable legal and regulatory requirements.

To put it more broadly, regulation of the safety of GM food is virtually nil, and research is scant and largely industry-funded. In a 2010 paper [PDF] in the journal Food Policy, researchers looked at all the papers on the health and nutritional effects of GM foods published in English between 1996 and 2009. Of the 94 studies they identified -- not a large number, given the surge of GMOs into our diets over that period -- 80 delivered "favorable" conclusions about the novel foods, while 10 had "negative" views and two were neutral. That sounds at first glance like a positive near-consensus around GMOs.

But then the researchers dug deeper and looked for industry ties. In 44 of the 94 total papers, one or more of the researchers had a financial or professional tie to the agrichemical industry. Of those 44, 43 had "positive" conclusions and one turned out "negative." Meanwhile, 37 of the studies were done by independent researchers. Of those, 27 came back positive, eight came back "negative," and two were "neutral." In other words, near-complete consensus reigns among industry-linked scientists as to the safety of GM foods. But among independent scientists, the issue is much more contested.

So where does all of this leave us? Obviously, in need of much more independent research. In April, a bit more trickled out from Quebec, Canada -- and again, the results are unsettling. The study, published in the journal Reproductive Toxicology, focused on corn engineered to possess a trait from the bacteria Bt, which is toxic to a range of insects. So-called Bt corn is extremely common in the United States; according to the USDA, upwards of 60 percent of corn planted here has it. Since its introduction in the '90s, its maker, Monsanto, has insisted that Bt corn must be safe, because the toxin embedded in it cannot survive the human digestive system.

The Quebec study (here's the abstract) casts serious doubt on that bedrock assumption. Researchers checked blood samples of 39 pregnant women and 30 non-pregnant women for the presence of the toxin. None were exposed directly to Bt, but all had conventional diets. The results: The Bt toxin showed up in 93 percent of pregnant women and 80 percent of their fetuses. It was also present in 69 percent of non-pregnant women in the study.

So, 15 years after the introduction of GMOs, we know that they pose no threat of immediate, spectacular harm. That is, they won't kill us suddenly. Whether they're killing us slowly -- contributing to long-term, chronic maladies -- remains anyone's guess.

Tom Philpott is Grist’s senior food and agriculture writer. You can follow his Twitter feed at twitter.com/tomphilpott.

The flying pips, shattered shells and wet shrapnel still haunt farmer Liu Mingsuo after an effort to chemically boost his fruit crop went spectacularly wrong.
Fields of watermelons exploded when he and other agricultural workers in eastern China mistakenly applied forchlorfenuron, a growth accelerator. The incident has become a focus of a Chinese media drive to expose the lax farming practices, shortcuts and excessive use of fertiliser behind a rash of food safety scandals.
It follows discoveries of the heavy metal cadmium in rice, toxic melamine in milk, arsenic in soy sauce, bleach in mushrooms, and the detergent borax in pork, added to make it resemble beef.
Compared to such cases of dangerous contamination, Liu's transgression was minor, but it has gained notoriety after being picked up by the state broadcaster, CCTV. The broadcaster blamed the bursting of the fruit on the legal chemical forchlorfenuron, which stimulates cell separation but often leaves melons misshapen and turns the seeds white.
The report said the farmers sprayed the fruit too late in the season and during wet conditions, which caused the melons to explode like "landmines". After losing three hectares (eight acres), Liu said he was unable to sleep because he could not shake the image of the fruit bursting. "On 7 May, I came out and counted 80 [burst watermelons] but by the afternoon it was 100," he said. "Two days later I didn't bother to count any more." About 20 farmers and 45 hectares around Danyang were affected. The fruit could not be sold and was instead fed to fish and pigs.
Farmers claim forchlorfenuron can bring the harvest forward by two weeks and increase the size and price of the fruit by more than 20%. Agricultural experts say forchlorfenuron has been widely used in China since the 1980s. Some said it was unsuitable for this fruit, but there was probably little health risk.
"In general we don't suggest chemicals with plant hormones be used on watermelons, as they are very sensitive. They might end up looking very strange and people will not want to buy them," said Cui Jian, director of the vegetable research institute at Qingdao Academy of Agricultural Science. "The taste won't be as good and storage is more difficult, but it should not harm anyone's health."
Environment groups say the overuse of agricultural chemicals is a problem that goes beyond growth stimulants.
Pan Jing of Greenpeace said farmers depended on fertilisers because many doubled as migrant workers and had less time for their crops. This dependency was promoted by state subsidies keeping fertilisers cheap. "The government is aware of the environmental problems caused by chemical fertiliser, but they are also concerned about food output."
Many farmers grow their own food separately from the chemically-raised crops they sell. "I feel there is nothing safe I can eat now because people are in too much of a hurry to make money," said Huang Zhanliang, a farmer in Hebei.
Concerns about food safety have lingered despite government promises to deal with the problem after six babies died and thousands became ill because of melamine-tainted milk in 2008.
The authorities appear to have mixed feelings about the role of the media and public opinion in naming and shaming culprits. In the wake of the melamine scandal, police jailed one of the parents, Zhao Lianhai, who had set up a website to expose the problem and appeal for justice. Recently, however, officials have encouraged coverage of food safety issues.
Zhang Yong, head of a new cabinet-level food safety commission, praised the media's "important watchdog role".
In the past week, the People's Daily website has run stories of human birth control chemicals being used on cucumber plants in Xian, China Daily has reported Sichuan peppers releasing red dye in water, and the Sina news portal revealed that barite powder had been injected into chickens in Guizhou to increase their weight.
More alarming still was a study by researchers at Nanjing Agricultural University that estimated a tenth of China's rice may be tainted with the cadmium, a heavy metal that can affect the nervous system. This caused a stir when it was published earlier this year in the pioneering Caixin magazine.
Many wary consumers choose to buy foreign products, which are seen as safer. But this is also vulnerable to mislabelling. The Fruit Industry Association of Guangdong province told reporters this week that "most 'imported' fruit are grown in China".

Scientists studying the effects of prenatal exposure to pesticides on the cognitive abilities of children have come to a troubling conclusion

New York City’s low-income neighborhoods and California’s Salinas Valley, where 80 percent of the United States’ lettuce is grown, could hardly be more different. But scientists have discovered that children growing up in these communities — one characterized by the rattle of subway trains, the other by acres of produce and vast sunny skies — share a pre-natal exposure to pesticides that appears to be affecting their ability to learn and succeed in school.

Three studies undertaken independently, but published simultaneously last month, show that prenatal exposure to organophosphate pesticides — sprayed on crops in the Salinas Valley and used in Harlem and the South Bronx to control cockroaches and other insects — can lower children’s IQ by an average of as much as 7 points. While this may not sound like a lot, it is more than enough to affect a child’s reading and math skills and cause behavioral problems with potentially long-lasting impacts, according to the studies.

“This is not trivial,” said Virginia Rauh, one of the study authors, speaking from Columbia University, where she is deputy director of the university’s Center for Children’s Environmental Health and professor of population and family health. What is particularly significant, she said, is that these studies involved so many children from such different communities, yet produced consistent evidence of the pesticides’ effects on cognitive skills and short-term memory.

Rauh said that the new studies were prompted by the long-standing awareness of the neurotoxicity of these pesticides on animals and the chemicals’ widespread use. Given science’s growing knowledge about the measurable effects of neurotoxic chemicals and elements, such as lead, on children’s cognition and behavior, the three recent studies were a logical next step in such research, Rauh explained.

The studies in New York and California were a continuation of research that has been ongoing for 12 years. Two of the studies, led by researchers at Columbia University and the Mount Sinai School of Medicine in New York City, looked at more than 660 children, ages six to nine, living in the South Bronx, Harlem, and other inner city neighborhoods. The New York mothers were exposed primarily indoors, as they lived in buildings where these pesticides were used in public areas and inside apartments. Previous studies of pregnant women in the same New York City neighborhoods had found organophosphate pesticides in all indoor air samples and in the majority of umbilical cord blood taken from these women when they gave birth.

Rauh and her colleagues began studying the New York City mothers before they gave birth. Organophosphate pesticide levels in several hundred pregnant women were measured and ranked, with the lowest levels being those where the pesticides were non-detectable. The researchers then evaluated their children’s cognitive and motor skills at one, two, and three years of age, finding that prenatal exposure to a common pesticide was associated with neurodevelopmental problems in the three-year-olds. The most recent study then tested the children at age seven. All the children were otherwise healthy and born to healthy, non-smoking mothers who were exposed to these pesticides while pregnant.

The New York studies found that for every increased increment of prenatal organophosphate pesticide exposure, the IQs of the children studied dropped by 1.4 percent and their working memory scores dropped by 2.8 percent. A key finding of the Columbia University study was that the relationship between pesticide exposure and IQ and working memory scores was linear and showed “no evidence for a threshold.” In other words, the greater the exposure, the greater the impact on cognition.

The third study, led by researchers at the University of California, Berkeley, looked at 329 children living in agricultural communities in the Salinas Valley, in Monterey County, the country’s top vegetable-producing region. The California mothers were predominantly Latino farmworkers, and their exposure resulted from living and working near where these chemicals were used agriculturally; when sprayed on crops, organophosphate pesticides can easily drift with the wind beyond their intended fields.

In 1999 and 2000, the California researchers measured levels of organophosphate pesticides in the blood of 601 pregnant women and initiated a long-term study that would follow their children at regular intervals. In those two years, more than half-a-million pounds of organophosphate pesticides were used in the Salinas Valley. More than 3.5 million pounds of organophosphate pesticides are used annually in California alone, sprayed on corn, strawberries, lettuce, broccoli, oranges, grapes, and almonds, among other products. The study authors note that in addition to ambient air exposures, both groups, in New York and California, were also likely exposed through pesticide residues in the food they ate.

As with the New York study, when researchers measured the IQ of the California children at age seven, those with the highest prenatal exposure scored as much as 7 points lower than the children with the lowest prenatal levels of pesticide exposure.

Bruce Lanphear, director of the Children’s Environmental Health Center at Cincinnati Children’s Hospital Medical Center, said in an interview that organophosphate pesticide exposure can impair development of the brain’s prefrontal cortex. Such damage actually shrinks this area of the brain and can lead to behavioral problems that include ADHD and later-life learning and social problems, including criminal behaviors, he said. This is also the part of the brain where short-term memory and instant gratification responses lie.

The study results are significant because they help show that while these children’s social circumstances — they came from low-income communities and families — can put them at an educational disadvantage, they also appear to be starting life with a preventable physiological disadvantage.

Organophosphates are well known neurotoxins — some were developed as nerve agents for use in chemical weapons — and work on insects by targeting the nervous system. They have been on the market since after World War II, but their use increased in the 1960s and 1970s, when they were promoted as an environmentally preferable, rapidly degrading alternative to more persistent organochloride pesticides, such as DDT. By the 1990s, organosphosphate pesticides were one of the world’s most widely used type of insecticides. Such pesticides include chlorpyrifos — used in household bug sprays, termite control, lawn care products, domestic pet flea and tick collars, and commercial agriculture — and malathion, used to control mosquitoes, fruit flies, and lice. Roughly 33 million pounds of organophosphate pesticides were used in the U.S. in 2007, the last year for which government statistics are available.

Rauh explained that when used indoors, these pesticides persist much longer than they do outside, where their degradation is hastened by sunlight and environmental disturbance.

“That organophosphate pesticides are not persistent does not mean that they’re not toxic,” explained Lanphear. And their widespread use has resulted in what he called “chronic exposure” of certain populations. There also is increasing evidence that organophosphate pesticides have adverse biological impacts that extend beyond their intended target insects. “We’re currently bringing new, very targeted types of pesticides onto the market without fully understanding their health effects,” said Amy Liebman, director of environmental and occupational health for the Migrant Clinicians Network.

But DowAgroSciences, which manufactures chlorpyrifos, says the pesticide is safe when used properly. “More than US $100 million has been spent examining the uses and impact of chlorpyrifos-containing products on human health and the environment,” the company says on its chlorpyrifos information website. “In terms of human health and safety, no pest control product has been more thoroughly studied.” Dow Chemical has called chlorpyrifos, which was first marketed by the company in 1965, “one of the great success stories in pest control.”

In addition to examining the outcomes of organophosphate pesticide exposures, the Mount Sinai research team looked at how the body responds biochemically to these alien compounds. As study co-author Stephanie Engel explained, she and her colleagues studied a gene that is key to how the body processes organophosphate pesticides. Several versions of this gene exist, and depending on which version a person possesses, it can have “relatively large effects on the metabolism of organophosphates,” said Engel, associate professor of epidemiology at the University of North Carolina’s Gillings School of Public Health. The study showed that the negative effects of pesticides occurred primarily in children whose mothers metabolize these pesticides less efficiently.

That effect indicates, Engel said, that the pesticides — rather than some unrelated outside factors — are causing the cognitive deficiencies. In response to the new studies, Dow and other chemical manufacturing groups have contended that “childhood IQ and development are strongly influenced by the complex interaction of many long-established factors (e.g., maternal intelligence, maternal education, quality of the home environment, etc.) which the researchers could only control for imperfectly.” Dow also criticized the studies’ data analysis and methodology, and said it would conduct a review of the findings.

Concern about the health effects of organophosphate pesticides, particularly on children, has been growing. As a result, the U.S. Environmental Protection Agency (EPA) has banned a number of these insecticides — including chlorpyrifos, diazanon, and methyl parathion — for residential use. Still, more than 30 organophosphate pesticides are currently registered for use in the United States. Many are now undergoing further evaluation by the EPA. Between 1997 and 2007, overall organophosphate pesticide use dropped by more than 50 percent in the U.S. With this decline came a drop in blood levels of these chemicals measured in biomonitoring studies, said Rauh.

But these bans do not affect agriculture and some other commercial uses, says Brenda Eskenazi, professor of public health at the University of California, Berkeley and lead author of the California study. Her study notes that despite the overall declines in organophosphate pesticide use, the quantity of these pesticides used in the Salinas Valley remained steady between 2001 and 2007, important years in the development of the children she studied. And continuing exposure is an important factor in these children’s health.

“For every increase in exposure there was an increase in impacts and for every decrease in exposure, a corresponding decrease in effect,” Eskenazi said. “We found there was no threshold or base limit of exposure that did not produce an effect.”

This is important to consider since it’s now known that organophosphate pesticides can cross the placenta and that prenatal development is very vulnerable to disturbance, including by synthetic chemicals.

Learning more about the specific mechanisms by which individual chemicals act — and and the effects they trigger — can point the way to which insecticides should be banned. In their next studies, Rauh and her colleagues plan to follow the children in their study group as they progress through school, using brain-imaging studies, blood analysis, and continued intellectual testing. Engel’s group plans to examine additional genetic factors that may help explain susceptibility to organophosphates.

Two generations after the U.S. stopped widely using the pesticides that Rachel Carson wrote about in Silent Spring, scientists are just beginning to get a distinct picture of how replacement pesticides are affecting the health of children. “We now have additional safety regulations for pesticides,” says Lanphear, ”but that doesn’t mean they’re safe.”